Circuit breaker with removable fuse unit having securing screws used for removal of the fuse unit



J. MAJCHER ETAL 3,319,025 CURING May 9, 1967 REMOVABLE FUSE UNIT HAVING SE E UNIT CIRCUIT BREAKER WITH SCREWS USED FOR REMOVAL OF THE FUS 2 Sheets-Sheet 1.

Filed May 28 INVENTORS John Mojcher and Robert H. Flick. BY

y ATTORNEY May 9, 1967 J. MAJCHER ETAL 3,319,025 CIRCUIT BREAKER WITH REMOVABLE FUSE UNIT HAVING SECURING SCREWS USED FOR REMOVAL OF THE FUSE UNIT Filed May 28. 1962 2 Sheets-Sheet 2 United States Patent 3,319,025 CIRCUIT BREAKER WITH REMOVABLE FUSE UNIT HAVING SECURING SCREWS USED FOR REMOVAL OF THE FUSE UNIT John Majcher, Chippewa Township, Beaver County, and Robert H. Flick, Brighton Township, Beaver County, Pa., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Filed May 28, 1962, Ser. No. 197,971 Claims. (Cl. 200-114) This invention relates generally to circuit interrupters and more particularly to circuit interrupters of the type comprising a low-cost circuit breaker and a fuse unit electrically connected in series relation with the circuit breaker to interrupt fault currents that exceed the interrupting capacity of the circuit breaker.

Certain features disclosed in this subject application are disclosed and claimed in the application Ser. No. 404,414, filed Oct. 16, 1964, which latter application is a continuation-in-part of this subject application.

An object of this invention is to provide an improved compact-1y constructed circuit interupter comprising a circuit breaker and a fuse unit connected in electrical series with the circuit breaker.

Another object of this invention is to provide an improved circuit interrupter comprising a circuit breaker and a removable fuse unit connected in electrical series with the circuit breaker with improved means for facilitating removal of the fuse unit from the circuit breaker.

The invention, both as to structure and operation, together with additional objects and advantages thereof, will be best understood from the following detailed description when read in conjunction with the accompanying drawings.

In said drawings:

FIGURE 1 is a top plan view of a circuit interrupter embodying principles of this invention;

FIG. 2 is a side elevational view, with parts broken away, of the circuit interrupter seen in FIG. 1;

FIG. 3 is a sectional view of the removable fuse unit taken generally along the line III-III of FIG. 1;

FIGS. 4 and 5 are elevationa-l and end views, respectively, of the barrier and tripping spring seen in FIGS. 1 and 2;

FIG. 6 is a top in FIG. 1;

FIG. 7 is an end view of the tripping bar seen in FIG. 6 looking in the direction of the arrows;

FIG. 8 is a top plan view of the trip bar seen in FIG. 1; and,

FIG. 9 is a sectional view taken along the line IX1X of FIG. 8.

Referring to the drawings, and particularly to FIGS. 1 and 2, there is shown therein a circuit interrupter 3 comprising a multi-pole circuit breaker 5 and a removable multipole fuse unit 7 connected in electrical series with the circuit breaker '5. The circuit breaker 5 comprises a housing comprising an insulating base 11 and an insulating cover 13 suitably connected to the base 11. A cirplan view of the tripping bar seen cuit breaker mechanism 14, of the type disclosed in Patent No. 2,989,606, issued June 20, 1961, to E. J. Walker et al., is supported within the housing 11, 13.

Each pole unit of the circuit interrupter 3 comprises a line terminal 15 and a load terminal 17 to enable connection of the circuit interrupter in an electrical circuit. A solderless terminal conductor 18 is disposed at the outer end of each of the terminals 15, 17 in a manner well known in the art.

The circuit breaker 5 is of the three-pole type, only the center pole being shown in FIG. 2. An operating ICC mechanism 19 common to all of the poles, is disposed in the center pole compartment. Each pole is provided with a trip device 21 similar to that seen in FIG. 2.

A stationary contact 22 is rigidly mounted on the innet end of each of the terminal conductors 17. A movable contact 23 is provided to cooperate with each of the stationary contacts 22. Each of the movable con tacts 23 is secured to a movable contact arm 25 that is pivotally mounted by means of a pin 29 on a switch arm 31. The switch arms 31 for the three pole units are secured to a common insulating tie bar 35 that is rotatably supported in the circuit breaker housing 11, 13. Springs (not shown) bias the contact arms 25 clockwise about the pins 29 to provide contact pressure in the closed position of the contact arms.

The operating mechanism 19 is disposed in the center pole unit and comprises a U-shaped operating lever 41 having its inner end portions pivoted on a suitable frame (not shown) that is mounted on the base 11. The operating lever 41 has an arcuate shield 47 mounted on the outer end thereof. A handle portion 49 extends out from the shield 47 through an opening 51 in the cover 13. The switch arm 31 for the center pole unit is operatively connected, by means of a toggle comprising links 53 and 55, to a releasable member or cradle 57 that is pivotally mounted on a pin 59 that is supported in the frame that supports the lever 41. The toggle links 53 and 55 are pivotally connected together by a knee pivot pin 61. The toggle link 53 is pivotally connected to the releasable member 57 by a pivot pin 63, and the toggle link 55 is pivotally connected by means of a pin 65 to the switch arm 31 for the center pole. Overcenter springs 67 are connected under tension between the knee pivot pin 61 of the toggle 53, 55 and the yoke portion of the U-shaped operating lever 41.

The contacts for all of the poles are manually closed and opened in a well-known manner by movement of the operating lever 41 to the on and off positions. Movement of the lever 41 to the on position straightens the toggle 53, 55 to move the switch .arm 31 for the center pole unit to the closed position. Since the switch arm for the center pole unit is connected to the tie bar 35, this movement rotates the tie bar 35 clockwise (FIG. 2) to move all of the switch arms 31 to the closed position.

" Reverse movement of the operating lever 41 to the off position causes collapse of the toggle 53, 55 to rotate the tie bar 35 counterclockwise and move all of the switch arms 31 to the open position.

The contacts are opened automatically, in response to an overload current above a predetermined value in any pole of the circuit breaker, by release of the cradle or releasable member 57. The cradle 57 is normally releasably held in an operative position by means of a latch mechanism indicatedgenerally at 71 which isactuated by the trip device 21 to release the cradle 57. When released, the cradle 57 rotates clockwise about its pivot 59 under the influence of the overcenter springs 67 causing collapse of the toggle 31 to the open position.

The latch mechanism 71 comprises a main latch 73 that.

is pivoted on a pin 75 that is supported in the frame that supports the lever 41. The main latch 73 is biased by a spring 77 in a clockwise unlatching direction. The main latch 73 is provided with a latching portion 79 that engages a latch portion 81 on the free or latching end of the cradle 57 to releasably hold the cradle in the operative position. The latch portion 81 is in-turned and faces generally toward the pivot 59 about which it moves. The

main latch 73 is releasably held in latching position by a latch that comprises a rotary shaft 83 that is pivotally mounted on the supporting frame. The main latch 73 is held in the latching position by the engagement of a 53, 55 to move all of the switch arms I part thereof with the shaft 83. This engagement is at a point on the cylindrical surface of the shaft 83 adjacent a notch (not shown) in the shaft 83. The purpose of the notch will be hereinafter specifically described. The latch 83 has an upwardly extending arm portion 89. An adjusting screw 93, which is threaded on the arm 89, is movable into engagement with a projection 97 on a common trip bar structure 98. The arm 98 and rotary'shaft 83 are biased by spring means to the latching position seen in FIG. 2.

The trip bar structure 98 comprises a trip bar 99 that is ofmolded insulating material. The projection 97 is molded integral with the trip bar 99 at a position adjacent the adjusting screw 93. The trip bar 99 is rotatably supported in the housing 11, 13 by means'of pins 101 (FIG. 8) molded in the ends thereof. Three projections 103, one for each pole unit, are molded integral with the trip bar 99.

The trip device 21 for each pole unit comprises a bimetal 105 that is supported on a conducting tab 107 by means of a screw 109. An adjusting screw 113 is threaded in a tab that is attached to the free end of the bimetal 105, and a generally U-shaped magnet member 115 is secured to the bimetal 105 intermediate the ends of the bimetal. A magnet member 117 is also connected to the conducting tab 107 by means of the screw 109. A leaf spring 119 having a contact 121 thereon is secured to the member 117 for a purpose to be hereinafter specifically described. A flexible conductor 123 is secured at one end to the bimetal 105, and at the other end to a terminal 125.

When a low persistent overload current occurs in any pole unit, the current carrying bimetal 105, for that pole unit, becomes heated and when heated a predetermined amount bends to the right. This movement, through the adjusting screw 113 and projection 103, rotates the trip bar 99 ina clockwise direction causing the projection 97 thereon to rotate the arm 89 and the rotary latch 83 clockwise until the latch 83 reaches a point where a portion of the main latch 73 snaps into the notch in the main latch 83 under the force of the springs 67. This movement releases the cradle or releasable member 57, whereupon the member 57 is rotated clockwise by means of the springs 67 to cause collapse of the toggle 53, 55 and opening of all of the contacts 22, 23.

The circuit breaker is trip-free in that the mechanism will operate to open the contacts when a tripping overload occurs even if the handle 49 is held in the closed position.

Upon the occurrence of an excessive overload current or a short circuit current, the magnet member 115 is attracted to the magnet member 117 bending the bimetal 105 to rotate the trip bar 99 to effect instantaneous tripping of the breaker. This bending of the bimetal 105 closes a contact (not shown) near the top of the bimetal 105 with the contact 121 that is supported on the leaf spring 119 forming a parallel shunt path for the current through the breaker. Since the resistance of the shunt path through the members 119 and 117 is les than the resistance through the bimetal 105, the major part of the current will be shunted around the bimetal, thus preventing overheating of the bimetal. By proper adjustment of the magnetic air gap and the distance between the shunting contacts, these contacts will close only on magnetic tripping and the breaker will trip on thermal tripping without closing the shunting contacts so that the thermal trip calibration is not affected by the shunting contacts.

Before the breaker contacts can be closed following an automatic opening operation, it is necessary to reset and relatch the mechanism. This is accomplished by moving the handle 49 counterclockwise to a position slightly past the full off position. During this movement, a projection 135 on the operating lever 41 engages a shoulder 137 on the cradle 57 to move the cradle counterclockwise about its pivot 59. Near the end of this movement, the lower rounded portion of the latch end 81 of the cradle 57 engages an outwardly extending portion of the bell-crank type main latch 73 to move the main latch 73 to the latching position. As soon as the latching shoulder of the main latch 73 clears the corner of the notch (not shown) of the cylindrical latch 83, a torsion spring restores the arm 89 and latch 83 to the normal latching position. The latching portion 79 of the latch 73 is then above the latch end 81 and it engages the latch end 81 of the cradle 57 to hold the cradle in the operative latched position seen in FIG. 2. Thereafter, the contacts can be closed and opened by operation of the handle 49 in the same manner previously described. 7

The multi-pole fuse unit 7 (FIGS 1-3) comprises a housing 131 of molded insulating material which housing comprises three compartments. A fuse 133is removably mounted in each of the fuse compartments. Each of the fuses 133 has a conducting member 135 connected to one end thereof and a conducting member 137 connected to the other end. A plug-in type connector 139 is connected to the conductor 135, and a plug-in type connector 141 is connected to the conductor 137. A spring-loaded plunger or actuator 145 is disposed at one end of each of the fuses 133. The plunger 145 is biased to move toward the right when the fuse blows. This plunger and baising means for operating it may be in one of the forms disclosed, for example, in the patent to Rawlins et al., Patent No. 2,435,844, issued Feb. 10, 1948.

The fuse unit 7 also comprises a tripping bar structure 147 (FIGS. l-3, 6, and 7), that is rotatably supported in the fuse unit housing 131 and is common to all three poles of the fuse unit. The tripping bar structure 147 is rotatably supported in notches in barriers (not shown) that separate adjacent poles in the fuse unit. Referring to FIGS. 6 and 7, the tripping bar structure 147 comprises an insulating tripping bar 149 having three arms 151 riveted thereto. An actuating arm 153 is riveted to the tripping bar 149 in a position adjacent an arm 155 (FIGS. 1 and 8) of the trip bar structure 98. As is seen in FIG. 3, a spring 157 is supported between the housing.

131 and the arm 153 to bias the tripping bar structure 147 in a clockwise (FIG. 3) direction. This clockwise movement of the tripping bar structure 147 is limited by engagement of the arm 153 with one of the fuses 133.

With the fuse unit 7 in place and the contacts 22, 23 in the closed position, the circuit through each pole unit of the multi-pole circuit interrupter 3 extends from the line terminal 15 (FIG. 2) through a tulip-type connector 163 that is mounted on the base 11, the plug-in type connector 139, the conductor 135 (FIG. 3), the fuse 133', the conductor 137, the plug-in type connector 141, a tulip-type connector 165 (FIG. 2) that is mounted on the base 11, the conductor 125,, the flexible conductor 123, the bimetal 105, the conducting support 107, a flexible conductor 167, the switch arm 31, the contact arm 25, the contacts 23, 22, to the load terminal conductor 17.

When a fuse 133 in any of the poles blows in response to a severe overload current, biasing means (not shown) within the fuse operates to move the plunger 145 (FIG. 3) to the right against the associated arm 151 to rotate the tripping bar structure 147 counterclockwise against the bias of the spring 157. During this movement, the arm 153 (FIGS. 1, 3, 6 and 7) on the tripping bar 149 engages the arm 155 (FIGS. 1, 8 and 9) on the common trip bar 99 (FIG. 1) rotating the trip bar 99 'in a clockwise (FIG. 2) direction, whereupon the projection 97 on the trip bar 99 operates to move the arm 89 and the latch 83 clockwise to effect a tripping operation of the circuit breaker 5 in the same manner hereinbefore described. The plunger or actuator 145 of the blown fuse 133 will remain in the position holding the tripping bar 149 in the tripped position to thereby hold the trip bar 99 and, therefore, the latch 83 in the tripped position. The circuit breaker cannot be relatched, and, therefore, it cannot be operated while the fuse unit, with a blown fuse therein, is in the connected position.

Improved means are provided for tripping the circuit breaker 5 when the fuse unit 7 is removed, and also for maintaining the breaker 5 in the tripped position when the fuse unit 7 is removed if the breaker has been tripped prior to removal of the fuse unit 7. Referring to FIGS. 1, 2, 4 and 5, an insulating barrier 171 which is provided to insulate part of the fuse unit 7 from the parts of the circuit breaker 5, is supported in suitable slots molded in the housing base 11. A metallic leaf spring 173 is mounted on the barrier 171 by means of rivets 175. As can be seen in FIG. 2, a projection 177 having a cam surface 179 thereon is molded integral with the insulating housing 131 of the fuse unit 7. When the fuse unit is moved down into the connected position seen in FIG. 2, the cam surface 179 on the projection 177 engages the leaf spring 173 to bias the leaf spring 173 to the inoperative position shown. When the fuse unit 7 is removed from the circuit breaker 5, the leaf spring 173 is released whereupon it springs to the right (FIG. 2) to engage an arm 1S1 (FIGS. 1 and 8) that is attached to the trip bar 99, rotating the trip bar 99 clockwise (FIG. 2) to effect tripping of the circuit breaker 5 in the same manner hereinbefore described if the circuit breaker 5 is in the closed position when the fuse unit 7 is removed. If the breaker 5 is in the open position when the fuse unit 7 is removed, the leaf spring 173 will move against the arm 181 to rotate the trip bar 99 clockwise to release the mechanism 19 to the tripped position to prevent closing of the breaker. As long as the fuse unit is removed, the spring 173 will maintain the trip bar 99 in the tripped position to prevent relatching of the breaker to thereby prevent .a closing operation of the breaker. If the breaker 5 is in the tripped position when the fuse unit 7 is removed, the spring 173 biasing against the arm 181 will maintain the trip bar 99 in the tripped position to prevent relatching of the circuit breaker 5 to thereby prevent a closing operation of the circuit breaker.

If the fuse unit 7 should be placed in position on the interrupter with a blown fuse still in the holder, the plunger or actuator 145 (FIG. 3) would hold the tripping bar structure 147 in a tripping position, and the arm 153 on the tripping bar structure 147 would engage the arm 155 (FIG. 1). on the trip bar 99 to bias the trip bar 99 t the tripped position to prevent resetting of the circuit breaker 5. Thus, when the spring 173 (FIG. 2) is biased to an inoperative position, the arm 153 on the tripping bar structure 147 will take over to maintain the trip bar 99 in the tripped position. Thus, the circuit interrupter cannot be operated when the fuse unit is replaced if the blown fuse is still in the fuse unit.

In order to facilitate removal of the fuse unit 7 from the circuit breaker 5, the fuse unit housing 131 is molded with two projections 185 on one side thereof and a projection 187 on the opposite side. As can be seen in FIGS. 1 and 2, the projections 185 are disposed over openings 189 in the housing which openings are provided to accommodate two of the terminals 19. The projection 187 is disposed over a depression or wellportion 191 in the housing, Thus, a worker can grasp the projections 185 and 187 with his fingers to lift the fuse unit 7 out of the circuit interrupter. The housing adjacent the depression or well-portion 191, can also be used as a fulcrum for a screwdriver or similar lever to lift housing 131. As can be seen in FIG. 2, when the fuse unit 7 is in the connected position, two plug-in type connectors 139, 141 engage in two tulip-connectors 163, 165 respectively, for each of the pole units. These connections are provided to have suflicient pressure to insure good electrical conductivity. Thus, it is often difficult for a worker to remove the fuse unit 7 from the circuit breaker by grasping the projections 185 and 187. Improved means, therefore, are provided to facilitate removal of the fuse unit 7 from the circuit interrupter when a worker has difiiculty in removing the fuse unit by grasping and lifting on the projections 185, 187.

Referring to FIGS. 1 and 2, securing means comprising two bolts 193 pass through suitable openings in the fuse unit 7 and are threaded into tapped metallic inserts 195 in the housing base 11 to secure the fuse unit 7 to the circuit breaker. When removal of the fuse unit 7 in the manner hereinbefore described is difficult, the bolts 193, which are removed from their mounting positions, are threaded into tapped metallic inserts 197 in the fuse unit housing 131. As can be seen in FIG. 2, the inserts 197 are so positioned that the major portion of each of the bolts 193 extends outward from the fuse unit 7 to permit easy grasp thereof by a worker who can grasp one bolt with each hand to lift the fuse unit 7 out of place. The bolts 193 can also be grasped by means of a suitable tool to enable a worker to more easily remove the fuse unit 7 from the circuit breaker 5.

From the foregoing, it will be understood that there is provided by this invention an improved compactly constructed circuit interrupter comprising a removable fuse unit. Tapped inserts are provided in the fuse unit housing to receive the same bolts that are used to mount the fuse unit to the circuit breaker. When these bolts are removed from their mounting positions and threaded into the tapped inserts, they can be grasped either manually or by means of a tool to enable a worker to more easily remove the fuse unit.

While the invention has been described in accordance with the provisions of the patent statutes, it is to be understood that various changes and modifications may be made in the structural details disclosed and in the arrangement of parts without departing from the spirit and scope of the invention.

We claim as our invention:

1. A circuit interrupting device comprising, in combination, a circuit breaker comprising cooperable contacts and means operable to open and close said contacts, a fuse unit having opening means therein and being connected in electrical series with said circuit breaker, securing means passing through said opening means in said fuse unit and threadedly engaging a portion of said circuit breaker to secure said fuse unit to said circuit breaker, said securing means being removable from said threaded engagement and from said opening means, and said fuse unit, having a portion adapted to receive said removed securing means in threaded engagement to facilitate removal of said fuse unit from said circuit breaker.

2. A circuit interrupting device comprising, in combination, a circuit breaker comprising an insulating housing and a circuit breaker mechanism supported within said housing, said circuit breaker mechanism comprising contact means and means operable to effect separation of said contact means, a fuse unit comprising fuse means removably connected in series relation with said separable contact means, a fuse holder for said fuse means supporting said fuse means and being removably positioned on said housing, at least one mounting bolt in threaded engagement with tapped means on said housing to secure said fuse holder to said housing, said fuse holder comprising tapped means, and said mounting bolt when removed from said housing being adapted to be screwed into said tapped means to facilitate removal of said fuse unit from said circuit breaker.

3. A circuit interrupting device comprising, in combination, a circuit breaker comprising an insulating housing and a circuit breaker mechanism supported within said housing, said circuit breaker mechanism comprising separable contact means and means operable to effect separation of said contact means, a fuse unit comprising fuse means connected in series relation with said separable contact means, an insulating fuse holder supporting said fuse means and being removably secured to said housing, two mounting bolts in threaded engagement with tapped means on said housing to secure said fuse holder to said 7 circuit breaker, said fuse holder having twotapped metallic inserts secured thereto, and said mountingbolts when removed from said housing being adapted to be screwed into said tapped metallic inserts to facilitate removal of said fuse unit from said circuit breaker.

4. A circuit interrupting device comprising a circuit breaker comprising an insulating housing and a circuitbreaker mechanism supported within said insulating housing, said circuit breaker mechanism comprising a pair of cooperable contacts, said insulating housing comprising a first front part, an operating handle extending from said first front part and being manually operable to open and close said contacts, a fuse unit comprising fuse means connected in electrical series with said pair of contacts, an insulating fuse holder supporting said fuse means, said insulating fuse holder comprising a second front part disposed on the same side of said circuit interrupting device as said first front part, securing means securing said fuse unit to said insulating housing and comprising a first tapped means unitary with said insulating housing, said securing means comprising an elongated mounting bolt, said insulating fuse holder having an opening therein, said elongated mounting bolt extending through said opening in said insulating fuse holder and having threaded means thereon threadedly engaging said first tapped means to removably secure said fuse unit to said insulating housing, said mounting bolt being externally accessible at said second front part, said insulating fuse holder having second tapped means at said second front part unitary therewith, and said threaded portion of said mounting bolt being adapted to mate with said second tapped means whereby when said mounting bolt is removed from said first tapped means and from said opening said mounting bolt can 'be screwed into said second tapped means in which position said mounting bolt can be grasped and pulled in order to remove said fuse unit from said insulating housing.

5. A circuit interrupting device comprising a circuit breaker comprising an insulating housing and a circuitbreaker mechanism supported within said housing, said circuit-breaker mechanism comprising a pair of cooperable contacts, said insulating housing comprising a first front part, an operating handle extending from said first front part of said insulating housing and being manually operable to open and close said contacts, a fuse unit comprising fuse means removably connected in electrical series with said pair of contacts, an insulating fuse holder, means physically connecting said fuse means with said fuse holder, said fuse holder comprising a second front part disposed on the same side of said interrupting device as said first front part, securing means securing said fuse means to said insulating housing and comprising a first pair of tapped metallic inserts secured to said insulating housing, two elongated mounting bolts, said insulating fuse holder having opening means therein, said two elongated mounting bolts extending through said opening means. in said insulating fuse holder and threadedly engaging said pair of tapped metallic inserts to removably secure said fuse unit to said insulating housing, said mounting bolts being externally accessible at said second front part, said insulating fuse holder having a second pair of tapped metallic inserts secured thereto at the front part thereof, said two mounting bolts being adapted to threadedly engage said second pair of tapped metallic inserts whereby when said mounting bolts are removed from said first pair of tapped metallic inserts and said opening means said mounting bolts can be screwed into said second pair of tapped metallic inserts in which position said mounting bolts can be grasped and pulled to remove said fuse unit.

References Cited by the Examiner UNITED STATES PATENTS 2,888,535 5/1959 Edmunds 200--116 2,900,101 8/1959 Clark 200-3 3,009,038 11/1961 Dorfman et al 200-116 3,015,709 1/1962 Bodenshatz 200-114 3,032,631 5/1962 Edmunds 2001l6 3,043,934 7/1962 Bodenschatz 200114 3,055,972 9/ 1962 Peterson 174-77 OTHER REFERENCES Catalog No. GD-10'l. Gateway Engineering Company, date of receipt March 20, 1961, pages 11 and 43.

BERNARD A. GILHEANY, Primary Examiner.

R. SCHAEFER, Examiner.

Assistant Examiners. 

1. A CIRCUIT INTERRUPTING DEVICE COMPRISING, IN COMBINATION, A CIRCUIT BREAKER COMPRISING COOPERABLE CONTACTS AND MEANS OPERABLE TO OPEN AND CLOSE SAID CONTACTS, A FUSE UNIT HAVING OPENING MEANS THEREIN AND BEING CONNECTED IN ELETRICAL SERIES WITH SAID CIRCUIT BREAKER, SECURING MEANS PASSING THROUGH SAID OPENING MEANS IN SAID FUSE UNIT AND THREADEDLY ENGAGING A PORTION OF SAID CIRCUIT BREAKER TO SECURE SAID FUSE UNIT TO SAID CIRCUIT BREAKER, SAID SECURING MEANS BEING REMOVABLE FROM SAID THREADED ENGAGEMENT AND FROM SAID OPENING MEANS, AND SAID FUSE UNIT, HAVING A PORTION ADAPTED TO RECEIVE SAID REMOVED SECURING MEANS IN THREADED ENGAGEMENT TO FACILITATE REMOVAL OF SAID FUSE UNIT FROM SAID CIRCUIT BREAKER. 